Slash "/" in test name

[gshiba]

My code (simplified)

@pytest.fixture(params=['/some/data1', '/some/data2'])
def dataframe(reqeust):
    return transform(request.param)

@pytest.mark.mpl_image_compare(baseline_dir=BASELINE_DIR)
def test_plot(dataframe):
    fig = my_plotter(dataframe)
    return fig

When I run pytest test_my_plotters.py --mpl --mpl-generate-path=baseline, I get something like (simplified):

IOError: [Errno 2] No such file or directory: '.../baseline/test_plot_/some/data1.png'

../venv/local/lib/python2.7/site-packages/matplotlib/backends/backend_agg.py:532: IOError

In short, print_png in matplotlib/backends/backend_agg.py is failing because the intermediate paths (.../some/...) is missing.

This work around seems to work (gshiba@3c8aa6e) but not sure if this is the right approach.

Thanks

[astrofrog]

I'm happy with the fix in #50, thanks!